In the field of vehicles, for example, a pulsating spring to which a bending load is applied (such as a spiral spring, a flat spiral spring, or a plate spring) is used, and it has been necessary to reduce the weight and size of the spring. For example, in order to reduce weight, it has been suggested that a fiber reinforced plastic spring (hereinafter referred to as an FRP spring) be used instead of a metallic spring.
For example, as shown in FIG. 8, in the case in which a pulsating bending load P is applied to a plate spring 51 which is supported by supporting portions 52, compressive stress is generated at an upper surface portion of a loaded side, and tensile stress is generated at a lower surface portion which is at the opposite side of the loaded side. It should be noted that reference symbol S is the neutral axis positioning at a center of thickness direction of the plate spring 51. In the case in which the FRP spring is used as the plate spring 51, cracking may occur at the compressive stress side.
In the FRP plate spring, simply the generation of small cracks may easily result in the spring breaking. In this case, as shown in FIG. 7, it may be broken, exhibiting brittleness. Therefore, there are a risk of scattering of broken pieces and a risk of damaging circumferential parts by the scattered broken pieces. In addition, since variation of load is large when there is breaking, ride comfort of vehicle may be badly affected.
In order to avoid scattering of broken pieces during breaking, a technique is disclosed in which a circumference of an end part of an energy absorbing member made of fiber reinforced resin is covered by a hollow cover (See Japanese Unexamined Patent Application Publication No. 2005-47387).
However, this technique is difficult to apply to a plate spring, and in addition, the hollow cover should be prepared as an additional member. Furthermore, it is difficult for this technique to reduce variation of load during breaking.